Chitotriosidase enzyme was measured in the sera of 50 subjects (30 patients with thalassemia major, 10 with thalassemia intermedia and 10 normal controls). It was elevated in 7 patients (23%) with thalassemia major, while it was not elevated in any of thalassemia intermedia patients or controls. Significant correlation was found between the enzyme activity and frequency of blood transfusion.